1. Field of the Invention
The present invention relates generally to sealant gels, and in particular relates to a sealant gel for an enclosure used in a telecommunication system.
2. Technical Background
Telecommunication systems typically have a number of locations where copper wires and/or optical fibers are terminated and/or that are connected (e.g., spliced) to other wires and/or optical fibers. These terminations and connections are preferably made within enclosures that have a sealed interior to prevent degradation of the connections or of the unspliced terminal ends of the fibers and/or wires from the surrounding environment.
For example, when fiber optic cables are spliced, the ends of the cables are often held within an enclosure called a “terminal seal” (or just “terminal” for short) to protect the ends of the cables and any connective equipment. Such terminals must cover and protect the cable ends from potential environmental damage caused by temperature variations, pressure variations, moisture, insects, dust, dirt, etc. The terminal necessarily includes one or more openings through which copper cables and/or fiber optic cables enter the terminal's interior region. Any openings so provided must be reliably sealed around the cables at the point of entry but still allow for manipulation of the cable by service personnel when necessary. At the same time, the terminals must be robust enough to securely hold the cables in place. The terminals may also need to withstand and maintain internal and external pressure differences due to environmental conditions, for example, temperature and pressure fluctuations or water immersion.
Some sealed enclosures rely on tape to close off any gaps leading to the enclosure interior formed between the particular cable and the opening through which it passes. Other sealed enclosures rely on a sealant gel to seal off any such gaps and to provide additional protection against the aforementioned environmental conditions.
For sealed enclosures deployed outdoors, any sealant gels used therein must be able to maintain their mechanical properties over the full range of outdoor environmental conditions. For example, a sealant gel must satisfy a number of environmental testing requirements including a heat-aging test wherein the gel is subject to a temperature of 90° C. for thirty days or 120° C. for a week. While it is relatively easy to formulate a soft polyurethane gel that has good viscoelastic properties at ambient (room) temperature, it is extremely difficult to form a soft polyurethane gel that can withstand 120° C. heat-aging for a week. The sealant gel must also perform well at subzero temperatures.
Some sealant gels are based on polyether-polyol. However, most polyether-polyol-based sealant gels degrade when exposed to high temperatures for an extended period. The degradation is a result of cross-linked network breakage, which causes the gel to melt and pool. Other sealant gels are formed from polyester based urethanes. However, such gels become brittle at subzero temperatures.
What is needed is as sealant gel for a telecommunication enclosure such as a terminal, wherein the gel maintains its key mechanical properties through environmental conditions, for example, over the full range between the high and low-temperature extremes the particular enclosures could experience when deployed in the field.